A polysilane has σ electrons forming Si—Si bonds in the main chain thereof, the σ electrons being entirely delocalized in the main chain skeleton in a similar manner to π electrons in a carbon conjugated system. In view of the feature, the polysilane is expected to be used as a conductive material or an optical semiconductor. Furthermore, a solvent-soluble polysilane such as poly(methylphenylsilane) is also used as a carrier for a transition metal in recent years. For example, Patent Document 1 discloses that a method in which a polysilane and a transition metal compound are dissolved or suspended in a good solvent for the polysilane, mixed them in the presence or absence of a reductant, and then gradually adding a poor solvent for the polysilane to the mixture to cause phase separation makes it possible to produce a polysilane-carrying transition metal which has a high catalytic activity and which is easy to be handle, collect, and recycle. However, dimethylpolysilane and diphenylpolysilane are insoluble in almost all solvents, and are not melt (see, for example, Non-Patent Document 1). Therefore, they are difficult to handle, and so have mostly not been used.
On the other hand, a method for obtaining metallic particles by applying electrolysis to a metallic salt solution and a method for obtaining metallic particles by adding a reductant to a metallic salt solution are conventionally known as methods for obtaining metallic particles from metallic ions. The method in which a reductant is used generally requires use of an aprotic solvent, because the use of a protic solvent causes problems in which metal cannot be reduced and a reductant is decomposed, due to the high-reactivity between the reductant and the protic solvent.
Patent Document 2 discloses a method for obtaining metallic particles using water which is a protic solvent. In the method, metallic ions in an aqueous medium are reduced using hydrophilic micelles as a reductant to obtain metallic monodispersed nanoparticles, the hydrophilic micelles being obtained using a block copolymer composed of a hydrophilic polymer and a polysilane and having an inner portion formed of the polysilane and a cross-linked shell portion. The hydrophilic micelles react with a protic solvent and thereby become soluble in water.